232 PM CST
SEVERAL SYSTEMS WILL AFFECT THE AREA THROUGH WEDNESDAY BRINGING MILD
WEATHER IN THE SHORT TERM FOLLOWED BY A NOTICEABLE COOL DOWN BY MID
WEEK. PERIODS OF RAIN WILL ALSO BECOME MORE LIKELY BEFORE THINGS DRY
OUT LATER IN THE WEEK. EARLY AFTERNOON WATER VAPOR IMAGERY SHOWS
UPPER LEVEL RIDGING ARCHING FROM PENNSYLVANIA BACK INTO SOUTHWESTERN
HUDSON BAY. A BROAD LONGWAVE TROUGH IS POSITIONED TO THE WEST FROM
SOUTHWEST AND SOUTH CENTRAL CANADA INTO THE WESTERN AND CENTRAL U.S.
WITH A SERIES OF EMBEDDED LOW CIRCULATIONS TRANSLATING THROUGH IT.
THE FIRST IS LIFTING NORTHWARD INTO CENTRAL MANITOBA AND WESTERN
ONTARIO WITH AN ASSOCIATED DEEP SURFACE LOW MOVING NORTHEASTWARD
FROM LAKES WINNIPEG AND MANITOBA. THE SECOND SIGNIFICANT CIRCULATION
IS DIGGING SOUTHEASTWARD ACROSS SOUTHERN CALIFORNIA AND NEVADA AND
WILL BRING A SURFACE LOW ACROSS THE FORECAST AREA LATER TUESDAY.
TONIGHT...THE MANITOBA SURFACE LOW WILL CONTINUE TO TRACK
NORTHEASTWARD INTO NW ONTARIO THIS EVENING AND WEAKEN. THE PRESSURE
GRADIENT WILL GRADUALLY WEAKEN ACROSS THE LOCAL AREA INTO THE
EVENING ALLOWING WINDS TO DIMINISH WITH GUSTS DROPPING OFF WITH
SUNSET. A WEAKENING COLD FRONTAL BOUNDARY WILL MOVE EASTWARD INTO
THE AREA THIS EVENING BUT WITH THE PARENT SURFACE LOW LIFTING
NORTHEASTWARD THE FRONT WILL MAKE SLOW PROGRESS AND EVENTUALLY STALL
OUT FROM SOUTHERN LAKE MICHIGAN SOUTHWESTWARD INTO FAR SOUTHEAST
IOWA OR NORTHEAST MISSOURI BY MONDAY MORNING. LITTLE IF ANY
RAIN/SPRINKLES ARE EXPECTED AS THE FRONT ENTERS THE AREA THIS
EVENING WITH DEEP LAYER MOISTURE STILL LACKING SOMEWHAT. A BETTER
PUSH OF GULF MOISTURE WILL POOL ALONG THE FRONT LATE TONIGHT AND
MONDAY HOWEVER. POPS WILL BE TRICKY LATER TONIGHT BUT AT THIS POINT
THE BEST CHANCES ARE EXPECTED TO BE CONFINED TO THE FAR SOUTHEASTERN
CWA OR SOUTH OF A LINE FROM GARY TO PONTIAC THOUGH THIS MAY BE TOO
FAR NORTHWEST.
MONDAY THROUGH TUESDAY NIGHT...THE WESTERN UPPER TROUGH WILL MAKE
ITS WAY INTO THE FOUR CORNERS MONDAY AFTERNOON WITH HEIGHT FALLS OUT
AHEAD OF IT SPAWNING SURFACE CYCLOGENESIS ACROSS THE TEXAS
PANHANDLE. AN INVERTED TROUGH WILL ALSO DEVELOP ALONG THE STALLED
COOL FRONTAL BOUNDARY AND EXTEND FROM THE DEVELOPING LOW
NORTHEASTWARD ACROSS SOUTHERN LAKE MICHIGAN BY MONDAY NIGHT.
SOUTHEASTERN AREAS WILL CONTINUE TO NEED AT LEAST LOW CHANCE POPS
MONDAY MORNING WITH CHANCES INCREASING THROUGH THE AFTERNOON AND
ESPECIALLY DURING THE EVENING AS ISENTROPIC ASCENT OVER THE FRONT
INCREASES AMID A 50+ KT LOW LEVEL JET AND THE MID LEVEL BAROCLINIC
ZONE TIGHTENS AS FRONTOGENESIS INCREASES. THE SURFACE LOW REMAIN
SOMEWHAT BROAD BUT MOVE NORTHEASTWARD TUESDAY WITH THE INVERTED
TROUGH REMAINING PARKED ACROSS THE AREA FROM NE TO SW. AS THE LOW
LIFTS NORTHEASTWARD RAIN CHANCES WILL SPREAD NORTHWARD ACROSS THE
REST OF THE AREA MONDAY EVENING AND MONDAY NIGHT. THE QUESTION THAT
REMAINS IS HOW FAR WEST THE LOW WILL TRACK AND THEREFORE HOW DOES
THE INVERTED TROUGH SHIFT FROM TUESDAY INTO TUESDAY NIGHT. ECMWF
REMAINS THE OUTLIER BEING DEEPER WITH THE UPPER TROUGH AND THEREFORE
SLOWER AND FURTHER WEST WITH THE SURFACE LOW WHILE THE GFS AND NAM
REMAIN FASTER AND FURTHER EAST. GFS AND SREF ENSEMBLE MEANS ARE MORE
IN LINE WITH THE NAM AND THE GFS IN TERMS OF TAKING THE LOW RIGHT
OVER THE AREA AND ACROSS LAKE MICHIGAN. WILL MAKE LITTLE CHANGE TO
THE FORECAST FROM MONDAY NIGHT THROUGH TUESDAY NIGHT IN TERMS OF
POPS WITH THE BEST CHANCES ALONG AND WEST OF INTERSTATE 57 THOUGH
AREAS TO THE EAST WILL CONTINUE TO SEE CHANCE AND LIKELY POPS DURING
THIS TIME. A FURTHER WESTWARD TRACK WOULD RESULT IN SOMEWHAT LOWER
POPS FOR THESE AREAS. HEAVY RAINFALL IS A CONCERN WITH PRECIPITABLE
WATER VALUES IN THE 1.25-1.5 INCH RANGE. ADD TO THIS THE THREAT FOR
THUNDERSTORMS AS A RIBBON OF INSTABILITY DEVELOPS EARLY TUESDAY AND
REMAINS IN PLACE INTO TUESDAY EVENING. THERE IS THE POTENTIAL FOR
MUCH OF THE CENTRAL AND WESTERN PART OF THE AREA OR WEST OF
ROUGHLY INTERSTATE 57 TO SEE 1-2 INCHES OF RAIN BETWEEN MONDAY AND
WEDNESDAY...WITH LOCALLY HIGHER AMOUNTS POSSIBLE. WILL NEED TO
MONITOR POTENTIAL FOR SOME STRONGER STORMS ACROSS THE SOUTHERN AND
SOUTHEASTERN CWA IF INSTABILITY CAN INCREASE AND STRONG LOW LEVEL
WINDS CAN BE BROUGHT TO THE SURFACE.
WEDNESDAY THROUGH SATURDAY...THE SURFACE LOW WILL CROSS THE AREA
TUESDAY NIGHT/EARLY WEDNESDAY BRINGING A SHARP COLD FRONT ACROSS THE
AREA WEDNESDAY MORNING. THE UPPER LOW WILL LIFT TO THE NORTHWEST OF
THE AREA WITH A PUNCH OF DRIER AIR EXPECTED BEHIND THE FRONT BUT
ANOTHER AREA OF PRECIPITATION WILL PROBABLY DEVELOP JUST AHEAD OF
THE UPPER TROUGH. AREAS NORTH OF INTERSTATE 80 LOOK TO STAND THE
BEST CHANCE FOR PRECIP BEHIND THE FRONT. H85 TEMPS WILL TUMBLE TO -2
OR -3 C BY WEDNESDAY EVENING AND PROBABLY FALL ANOTHER DEGREE OR TWO
BY THURSDAY MORNING. A MUCH DRIER ATMOSPHERE LOOKS TO BE IN PLACE BY
WEDNESDAY AFTERNOON BUT THE CYCLONIC FLOW MAY SUPPORT SOME PRECIP
DEVELOPMENT...WHICH IF IT DOES OCCUR...WOULD PROBABLY BE A MIX OF
RAIN AND SNOW. HOWEVER...AT THIS POINT IT LOOKS LIKE THIS WOULD BE A
SLIM CHANCE. ASSUMING THE SYSTEM DOES NOT SLOW TOO MUCH THEN HIGHS
WEDNESDAY WOULD PROBABLY BE IN THE LOW 50S AT BEST DURING THE
MORNING AND PROBABLY FALL BACK INTO THE 40S DURING THE AFTERNOON
WITH HIGHS IN THE 40S THURSDAY.
HIGH PRESSURE WILL CREST THE AREA THURSDAY NIGHT WITH WARM ADVECTION
IN SOUTHERLY FLOW RETURNING FRIDAY LEADING TO MODERATING TEMPS. MUCH
OF THE WEEKEND MAY END UP DRY WITH LOW PRESSURE DEVELOPING TO THE
SOUTH AND WEST AT SOME POINT LATE IN THE WEEKEND OR EARLY NEXT WEEK
WITH LITTLE MODEL AGREEMENT BY THIS TIME.
MDB
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 08Z...
* VARIABLE CIGS WITH AREAS MVFR.
* CHANCE FOR MVFR BR NEAR DAYBREAK UNDER ANY BREAKS IN CLOUDS.
* LIGHT WINDS TRANSITIONING FROM SW TO NE AS COLD FRONT CONTINUES
TO SLOWLY SINK SWRD ACROSS NE IL.
* CHANCE SHRA AFTER 23Z MON.
//DISCUSSION...UPDATED 06Z...
A WEAKENING COLD FRONT IS SLOWLY INCHING EAST INTO NORTHERN IL.
AHEAD OF THIS BOUNDARY A STREAM OF MOISTURE CONTINUES TO ENVELOP
THE AREA...LEADING TO VARIABLE CLOUD COVER THAT IS UNDULATING IN
HEIGHT BETWEEN 2K TO 4K FT. THIS TREND HAS PREVAILED THROUGH THE
PAST SIX HOURS AND SHOULD THROUGH DAYBREAK WITH ONLY A SLIGHT
FALLING IN HEIGHT EXPECTED. SUCH A DECREASE HAS BEEN SEEN JUST
AHEAD OF THE BOUNDARY. SCATTERING MAY BE MOST FAVORED ACROSS RFD
LATE TONIGHT AS THE BOUNDARY SHIFTS THROUGH. THIS MAY PROMOTE FOG
DEVELOPMENT AND SPORADIC LOWER VISIBILITY IN LIGHT FOG HAS BEEN
SEEN IN CLOUD HOLES UPSTREAM. AS THE BOUNDARY SHIFTS THROUGH AND
THEN STALLS...WIND SPEEDS WILL BECOME LIGHTER AT AREA TAF SITES BY
DAYBREAK AND THROUGH MUCH OF MONDAY. THE DIRECTION ALSO BECOMES
CHALLENGING TO FORECAST...WITH VARIABLE CONDITIONS LIKELY AT
TIMES. MOIST AIR WILL BEGIN TO OVERRIDE THE FRONT ONCE AGAIN BY LATE
MONDAY AFTERNOON INTO MONDAY NIGHT AND FAVOR AN INCREASE IN
SHOWERS ACROSS CENTRAL IL...GRADUALLY WORKING INTO NORTHERN IL AND
NORTHWEST IN LIKELY LATER MONDAY NIGHT. MVFR CONDITIONS ARE LIKELY
IN ANY OF THIS SHOWER ACTIVITY LATER IN THE NIGHT.
//ORD AND MDW CONFIDENCE...UPDATED 08Z...
* HIGH CONFIDENCE IN VARIABLE CEILING HEIGHTS BETWEEN 2500 AND
4500 FT THROUGH THE NIGHT...WITH LOW CONFIDENCE IN SPECIFIC MVFR
TIMING.
* LOW CONFIDENCE IN DEVELOPMENT AND TIMING OF ANY MVFR FOG
DEVELOPMENT EARLY MONDAY MORNING...DUE TO VARIABILITY IN CLOUD
COVER BREAKS.
* HIGH CONFIDENCE IN VARIABLE WINDS AT TIMES DURING THE DAY
MONDAY.
* LOW CONFIDENCE IN RAIN SHOWERS BEFORE 06Z TUESDAY...THEN
CONFIDENCE INCREASES MARKEDLY BETWEEN 06Z AND 12Z TUESDAY.
//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...
TUESDAY...MORNING MVFR PROBABLE. SHOWERS EXPECTED WITH STORMS
POSSIBLE INTO THE NIGHT. GUSTY SOUTH TO SOUTHWEST WINDS.
WEDNESDAY...MORNING MVFR POSSIBLE. CHANCE OF SHOWERS. GUSTY WEST
TO NORTHWEST WINDS.
THURSDAY...VFR.
FRIDAY...VFR.
SATURDAY...VFR.
MTF/TRS
&&
.MARINE...
323 AM CST
WINDS HAVE GRADUALLY BEEN TRENDING DOWN THROUGH THE NIGHT AND
EARLY MORNING HOURS...MORESO OVER THE SOUTHERN HALF OF THE LAKE
WHERE HIGH PRESSURE IS BEGINNING TO ENCROACH FROM THE SOUTH.
ACROSS THE NORTH...BREEZY CONDITIONS ARE STILL BEING OBSERVED BUT
WILL CONTINUE TO TAPER AS THE LOW OVER ONTARIO CONTINUES TO LIFT
AWAY FROM THE REGION. THE NEXT WEATHER SYSTEM OF CONCERN WILL
BEGIN TO TAKE SHAPE OVER THE CENTRAL PLAINS OVERNIGHT
TONIGHT...AND QUICKLY LIFT NORTHEAST REACHING LAKE MICHIGAN LATE
TUESDAY NIGHT. MODELS CONTINUE TO SHOW MODEST DIFFERENCES BETWEEN
THE TRACK AND INTENSITY OF THIS LOW...THUS THE IS A FAIR DEGREE OF
UNCERTAINTY IN TIMING THE WIND SHIFTS AND WIND MAGNITUDES. DOES
APPEAR THAT THE FRONTAL BOUNDARY WILL STALL ACROSS SOUTHERN OR
CENTRAL PORTIONS OF THE LAKE TUESDAY WITH A BAND OF LIGHTER
WINDS...BUT WINDS SHOULD SHARPLY INCREASE TO THE SOUTH OR NORTH OF
THE FRONTAL ZONE. AS THE LOW PASSES NORTHEAST OF THE LAKE
WEDNESDAY...A TRAILING COLD FRONT WILL SWITCH WINDS AROUND TO THE
NORTHWEST...WITH WINDS FURTHER INCREASING...AND LOW END GALES
POSSIBLE. WINDS WILL TREND BACK DOWN THURSDAY AS HIGH PRESSURE
APPROACHES AND MOVES ACROSS THE LAKE ON FRIDAY. BMD
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
